Paris: Rescue workers searched throughout the night for two people missing after an explosion ripped through an apartment building outside Paris, killing six and reducing half a residential block to rubble. Among the victims were a 10-year-old boy and a mother and two children aged 14 and 18.

The bodies of a 45-year-old woman and another adult were also recovered from the remains of the four-storey building in the northeastern suburb of Rosny-sous-Bois.

Firefighters were combing the wreckage for two other missing people, Mayor Claude Capillon said. "There's still hope," said Capillon, stressing that the search and rescue operation would continue until the missing persons were accounted for.

However local prefect Philippe Galli cautioned that "the more time that passes the more the chances of finding survivors drops."

Some 40 firefighters and other rescue workers toiled throughout Sunday night among the ruins of the building with the help of sniffer dogs.

The building was practically scythed in two. Wallpaper, toilet seats, family photos and other everyday items were left open to the elements.

Neighbours said the blast, which happened at around 7:00 am (0500 GMT) Sunday, was strong enough to shake buildings some 100 metres (yards) away.'Trembling with fear' Early indications were that it was an accidental gas explosion. "Our house moved, we were trembling from fear," said Pauline, a neighbour, adding that the explosion was so loud that "our ears were ringing".

Ghislaine Poletto, 55, who lives about 50 metres away from the collapsed building, said she "jumped into her trousers" and rushed to the site, where together with neighbours "we managed to pull two children out".

One of the children was "protected by a mattress and a board above his head, which saved his life," she said.

Firefighters said 11 people were injured in the explosion, four of them seriously. Two of the injured were children aged 10 and 13.

Gaetan de Raucourt, head of the Paris firefighting department, said there was still hope that occupants had found "pockets of air" amid the wood and dusty concrete rubble, which was piled a storey high and fanned out into the street.

"People might be sheltering there. We still have hope of finding survivors," he said.

Emergency crew chief Bernard Tourneur said the search would continue for at least 24 hours with care, since the remainder of the building left standing "is threatening to cave in".

Interior Minister Bernard Cazeneuve, who visited the scene, and police initially pointed to a gas leak as a likely cause of the blast.

A fire service commander, Gabriel Plus, said gas and electricity works had been ongoing at the site, but would not confirm their link to the disaster.

GRDF, the company in charge of delivering gas to homes, told AFP that "no leaks had been reported previously" in the area.

Neighbour Maryline Yyvon suggested the explosion was indeed the result of a gas leak. "They'd been digging under the sidewalk just in front of the building," she told AFP.

"Given the force of explosion, it wasn't just a gas canister, that's for sure," she said.

Deputy Mayor Serge Deneulin said the building dates from the 1970s and was "in perfect shape".

City officials set up a makeshift shelter in a nearby school with an on-site medical team for families hit by the blast.